In the field of shipbuilding, the reduction of energy consumption is becoming increasingly significant in view of the global economic crisis and the intensification of environmental problems.
One important factor that determines fuel requirements for the propulsion of a vessel is that of the wave making and frictional resistances it encounters. An ongoing attempt has thereby arisen to reduce such wave making and frictional resistances experienced by the vessels and afford an improvement in their propulsion through the solid mass of water they have to cross. By way of example, a bulb or ball configuration of the bow section of the hull has been widely used in the past to reduce wave making resistance and especially to reduce the height of the bow wave.
However, the frontal surface of the vessel, i.e. the surface area of the bow that comes in contact with water during propulsion of the vessel is an extensive area, and taking into account that the propulsion resistance is proportional to the square of the speed of the vessel, it follows that a correspondingly increased horsepower is required to overcome this resistance and provide propulsion of the vessel at the rated speed for which it has been designed.
WO-92/22456 (Petromanolakis Em.) has proposed a duct mounted at the bow of a vessel and extending at a height above and below the waterline thereof, such duct achieving a reduction of the wave making resistance during propulsion of the vessel as the vessel hits onto the water mass through the duct and not through the entire frontal surface thereof. Such a wave making resistance and energy consumption reducing duct has been optimized in subsequent patent applications wherein an increased differentiation of the flow through the duct in relation to the flow outside it has been attained.
In particular, WO-2013/011332 (Petromanolakis Em. et al) has disclosed a hydrodynamic duct mounted at the bow of a vessel, comprising a horizontal wall portion and two lateral wall portions, whereby the flow through the duct acquires substantially different characteristics from the flow outside it and thereby wave making and frictional resistances are reduced and the fuel conventionally required for the propulsion of the vessel is reduced accordingly. The duct is arranged with the Center of Low Pressure corresponding to a zero angle of attack onto the horizontal wall portion being located in the region of generation of the first bow wave and with the Centers of Low Pressure of the lateral wall portions in the region of connection thereof with the horizontal wall portion being located in a selected position between the Center of Low Pressure of the horizontal wall portion and up to or slightly forwardly the leading edge thereof. Further with a scope of overcoming drawbacks and deficiencies of the prior art structural design parameters of the stem hydrodynamic duct have been proposed that allow optimization of the performance of the duct. In particular selective combinations are being proposed in the manufacturing parameters of the horizontal wall portion and of the lateral wall portions of the duct, wherein those parameters in the geometry of the wall portions of the duct, which determine the lift coefficient CL and drag coefficient CD are being considered with a scope of obtaining optimization of the ratio CL/CD for both the horizontal and for the lateral wall portions of the duct, as well as of obtaining optimization of the ratio of the lift coefficient CL of the horizontal wall to the lift coefficient CL of the lateral walls of the duct in correspondence with the specific nominal speed of propulsion of the vessel and the geometry of the bow.
It has however been observed that whilst the herein above proposed parametric design of the duct has led to significant improvements, such improvements having been confirmed through tests that have been carried out in models of different types of vessels (yachts, containers, bulk carriers and frigates) equipped with the hydrodynamic duct, the variation evident in the results obtained with the abovementioned different types of vessels has underlined the need of further work in the parametric design of the duct, wherein such design process is required to take into account the varying parameters of the configuration and of the geometry of each particular bow and further of the variable loading of the vessel, whereby the bow has to be designed in a manner such as to ensure optimal performance of the bow-duct combination thereby optimizing the eventual outcome of reduced horsepower requirements for the propulsion of the vessel and of reduced fuel consumption accordingly.
By way of example, whilst it has been found that the positioning of the duct at the bow of the vessel necessarily contributes to achieving an economically advantageous cruising, further also reducing the acceleration in the vertical movement of the bow thereby achieving a higher average speed of cruising, it is hereby considered that one reason for the differentiation of results obtained in the above tests is the diversity in the cooperation of the proposed duct with the vessel, as the flow exiting the duct impacts onto the sides of the bow and/or of the bulb, such impact creating obvious losses and contributing to the minimization of the beneficial effect of the duct.
Another reason for the differentiation in the continuity of the performance of the duct in the different tests that have been carried out is the varying loading condition of the vessel that differentiates the draught, i.e. the depth of immersion of the vessel in water, thereby changing the active range of the duct, such problem being particularly evident in container vessels wherein draught varies significantly in the extreme conditions of the ship without cargo and of the ship in a fully loaded condition.
It has also been observed that whilst the performance of the bulb in a vessel is satisfactory as long as the vessel travels at the nominal speed thereof and it is being reduced at lower speeds due to the concurrent change in Fn, the provision of the duct of the invention ensures a satisfactory performance also at speeds inferior than the designed nominal speed (economic speed) and at any Fn value whatsoever.
It is therefore a main object of the present invention to efficiently overcome the aforementioned drawbacks and deficiencies of the prior art and to propose structural design parameters of the hydrodynamic duct which will allow optimization of the performance thereof in conjunction with the functionally interdependent parameters of the configuration and geometry of the bow of the vessel, as well as with the varying loading conditions thereof.
It is therefore an object of the invention to provide a functional design of the bow of the vessel that is compatible with the installation of the hydrodynamic water flow management duct mounted thereupon with the waterlines being either rectilinear or convex rather than concave, always at a certain angle relative to the centerline of the vessel, so as to avoid the flow impacting onto a concave curvature of hollow curved sides of the bow and being entrapped therein, since such impacting and entrapping of the flow would undesirably contribute towards decelerating the vessel. A smooth flow at the outlet of the duct is therefore obtained with a rectilinear or convex rather than concave configuration of the bow sides and losses associated with the impacting of this flow onto the bow walls and/or onto the bulb are minimized.
Especially in ships fitted with a bulb, it is herein proposed a design that ensures coordination of the beneficial results of the bulb with the beneficial results of the duct in order to maximize cruising performance and minimize fuel consumption. It is in particular an object of the invention with particular application in vessels equipped with a bulb, to position the bulb in a manner such that the upper part thereof would be located not far beneath, but close to the load line and so that the stagnation point of the bulb would be located within the flow passing through the duct of the invention, wherein the proposed design contributes in the flow passing through the duct to influence all upwardly directed wave making vectors and some of the downwardly directed wave making vectors, thereby improving the flow at the sides of the vessel.
A further object of the invention is to propose the hydrodynamic water flow management duct at the bow of a vessel with a capacity of vertical movement so as to optimize the beneficial influence of the duct under varying conditions of draught of the vessel that depend on the loading thereof and on the consumption of consumables.
Another object of the invention is to propose the abovementioned vertically displaceable hydrodynamic water flow management duct at the bow of a vessel preferably provided with means that ensure its watertight abutment onto the side walls of the bow of the vessel thereby maintaining unaltered the characteristics of the flow within the duct. It is in particular an object of the invention to propose an embodiment with the duct mounted onto a plate covering the bow of the vessel, such plate extending in the longitudinal direction of the vessel and covering part or the entire length of the horizontal wall portion of the duct and moving together with the horizontal and the lateral walls of the duct thereby ensuring the watertight properties within the duct.
Another object of the invention for the case wherein the aforementioned plates covering the side walls of the bow are not provided, is to propose an alternative embodiment according to which the watertight abutment of the vertically displaceable horizontal wall portion of the duct onto the side walls of the bow is being achieved by using suitable sealing mechanisms, such as by way of example chambers being filled with air or other fluid medium or solid fixtures, made from rubber or other material, such chambers or solid fixtures or other types of means of watertight abutment being pushed towards the side walls of the bow, which are being installed either at the ends of the horizontal wall portion of the duct or at appropriate predetermined positions of the side walls of the bow and being actuated by hydraulic or pneumatic or mechanical or electrical mechanisms are being brought in a watertight abutment condition of the vertically displaceable horizontal wall portion of the duct onto the sides of the bow of the vessel. Similar sealing mechanisms for a watertight abutment can be used in the case where plates are employed for covering part of the length at the ends of the horizontal wall portion of the duct, whereby such sealing mechanisms are installed within the horizontal wall portion and are used to provide a watertight fitting onto the side walls of the bow for the remaining portion of the length of the horizontal wall portion extending beyond the length thereof that is covered by the plates.
Another object of the invention is to propose the horizontal wall portion of the abovementioned duct for the management of flow at the bow of a vessel provided with sheet metal plates or blades on either side thereof, such sheet metal plates or blades extending underneath the duct and converging towards the bow of the vessel, wherein these sheet metal plates or blades on either side of the horizontal wall portion contribute in the reduction of the stresses being exerted thereupon during the vertical movements of the bow due to sea waves.
It is another object of the invention to propose alternative arrangements of the horizontal wall portion of the hydrodynamic duct in relation to the bow of the vessel in order to optimize its performance
In particular an object of the invention is to propose the hydrodynamic duct with an imaginary line passing through the leading edge of the horizontal wall portion thereof forming an angle (a) on either side of the axis of symmetry of the vessel and with an imaginary line passing through the trailing edge of the horizontal wall portion forming an angle (b) on either side of the axis of symmetry, i.e. the centerline of the vessel.
Another object of the invention is to propose an embodiment wherein the horizontal wall portion of the hydrodynamic duct extends in a direction parallel to or at a certain slope, upwardly or downwardly, relatively to the horizontal level of the waterline on either side of the axis of symmetry of the vessel.
Another object of the invention is to propose a suitable geometry of the lateral walls of the hydrodynamic duct in relation to the bow of the vessel and in conjunction with the aforementioned positions of the horizontal wall portion with a scope of optimizing the performance of the duct and in particular to propose the hydrodynamic duct with lateral walls formed so that the horizontal section thereof will follow the geometry and in particular the flare of the bow with the trailing edge of each horizontal section of the lateral walls being maintained at a constant equal distance from the side walls of the bow, such distance being defined by the perpendicular taken from the trailing edge of the lateral walls that corresponds to each particular waterline.
A further object of the invention is, mainly for aesthetic reasons which are particularly important design parameters for recreation vessels (yachts, etc.), but also in other types of vessels, to ensure conditions were in order not to adversely affect the aesthetics of the vessel, the lateral walls of the duct of the invention are located approximately at the height of the waterline of the vessel when it is stationary in the port and in order to achieve this result it is being suggested that a portion of these lateral walls is coated with a hydrofoil section with an analogous configuration or that these lateral walls are provided with appropriately shaped plate extensions, whereby the abovementioned hydrofoil sections or plate extensions can move, when the vessel leaves the port and cruises, by sliding along the vertical direction so that the lateral walls may under any circumstances be located sufficiently above the waterline level to ensure the desired differentiated flow conditions within the duct.
A further object of the invention serving the same aforementioned goal of aesthetics is to propose the duct of the invention comprising parts of or the entire lateral walls and/or of the horizontal wall portion being selectively made invisible, whereby the hidden part of the lateral walls and/or of the horizontal wall portion retract within the vessel and project outwardly thereof through appropriate driving mechanisms. It is in particular an object of the invention to propose a design of the hydrodynamic duct with parts or with the entire lateral walls encased within the vessel along the side walls of the bow and being adapted to move downwardly when they must be brought in operating condition, whereby they “snap” into recesses or protrusions of either the horizontally extending retractable portions of the horizontal wall portion or directly into the recesses or protrusions of the horizontal wall portion.
A further object of the invention is to provide additional one or more blades extending parallel to and underlying the horizontally oriented or inclined wall portion of the duct of the invention, such blades having the same or different hydrofoil section as the horizontally oriented or inclined wall portion of the duct, wherein the space provided in between the horizontally oriented or inclined wall portion and the underlying additional blade is either being covered or is not being covered by lateral blades, wherein the objective of the proposed additional one or more blades is the increase in the speed of the incoming flow to the duct of the invention and therefore the enhanced further diversification of the characteristics of flow within the duct from the flow outside the same.
An additional object of the invention is to provide a configuration of the horizontal wall portion of the duct with an arrangement of projections, which reinforce the profile of the horizontal wall portion and in addition act as guides for the projection of appropriate sheet laminates through slots of the horizontal blade, such sheet laminates extending forwardly the leading edge and/or rearwardly the trailing edge thereof when a further control of the vertical acceleration vectors of the flow is required and when the lift coefficient CL is sought to be suitably positioned in the resultant new geometry of the horizontal wall portion of the duct in order to optimize flow characteristics within the duct.
With the design parameters and combinations of the same proposed in the present invention, solutions are provided for the design of the hydrodynamic duct functionally interdependent with the design of the bow of the vessel whereupon it is being mounted, thereby achieving optimal advantageous differentiation of the flow characteristics within the duct from the flow outside it and accordingly obtain reduced wave making and frictional resistances during propulsion and a consequent reduction in horsepower requirements and in fuel consumption.
These and other objects, features and advantages of the present invention will become apparent in the detailed description of preferred embodiments.